Cooled mirrors are well known in the art. These mirrors are used in conjunction with laser beams having extremely high energies such as those used in industrial laser welding and the Strategic Defense Initiative. In operation, these mirrors experience tremendous thermal loading which, if uncooled, would cause unacceptable amounts of mirror distortion. Typically, prior art cooled mirrors comprise a substrate and optically reflective surface with a heat exchanger positioned therebetween. Heat deposited by the incident laser beam is transported away from the reflective surface by a liquid coolant flowing through the heat exchanger, exiting the mirror by way of the substrate.
For high performance applications the substrate must provide a stable reference for the optical surface and provide attachment points for mounting. The substrate structure must also incorporate high stiffness construction to resist deformations caused by thermal growth of the heat exchanger. Coolant must be supplied to the heat exchanger at many locations, mandating extensive manifolding within the substrate. This configuration produces an unacceptable amount of heating of the substrate due to heat transfer between warmed coolant returning from the the heat exchanger and the substrate. The substrate is relatively massive and its temperature responds slowly to heat input. Slow thermal responsivity produces mirror distortions that do not stabilize during operation.
Prior art laser mirror designs have employed several techniques to shield the substrate from heated coolant returning from the heat exchanger. Typical of these are insulated inserts positioned in the coolant return ports. Mirror substrates constructed in this fashion are complex, requiring many separate components and assembly steps.